1. Field of the Invention
The present invention relates to novel photoresist monomers, polymers formed therefrom, and photoresist compositions containing the same. In particular, the present invention is directed to a bicyclic photoresist monomer compound comprising both amine and protecting group. Moreover, the present invention is also directed to polymers, and a photoresist compositions derived from the bicyclic photoresist monomers, and uses thereof, such as in photolithography processes using a DUV (deep ultraviolet) light source for preparing highly integrated semiconductor devices.
2. Description of the Background Art
Recently, chemical amplification type DUV photoresists have been investigated for achieving a high sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are typically prepared by blending a photoacid generator and a matrix resin polymer having an acid labile group. The resolution of a lithography process depends, among others, on the wavelength of the light source, i.e., shorter the wavelength, smaller the pattern formation.
In general, a useful photoresist (hereinafter, abbreviated to as xe2x80x9cPRxe2x80x9d) has a variety of desired characteristics, such as an excellent etching resistance, heat resistance and adhesiveness. Moreover, the photoresist should be easily developable in a readily available developing solution, such as 2.38% aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a photoresist polymer, especially DUV photoresist, which meets all of these desired characteristics. For example, a polymer having a polyacrylate polymer backbone are readily available, but it has a poor etching resistance and is difficult to develop. In order to increase its etching resistance, several groups have added an alicyclic unit to the polymer backbone. However, photoresist copolymers comprising entirely of an alicyclic polymer backbone is difficult to form.
To solve some of the problems described above, Bell Research Center developed a polymer having the following chemical formula: 
where the polymer backbone is substituted with a norbornene, an acrylate and a maleic anhydride unit. Unfortunately, even in the unexposed regions, the maleic anhydride moiety (xe2x80x98Axe2x80x99 portion) dissolves readily in 2.38 wt % aqueous TMAH solution. Therefore, in order to inhibit the dissolution of the polymer in the unexposed section, the ratio of xe2x80x98Yxe2x80x99 portion having tert-butyl substituent must be increased, but this increase results in a relative decrease in the xe2x80x98Zxe2x80x99 portion, which is responsible for the adhesiveness of the photoresist polymer. This decrease in the relative amount of the xe2x80x98Zxe2x80x99 portion may result in separation of the photoresist from the substrate during a pattern formation.
In order to circumvent the dissolution problem of maleic anhydride, cholesterol type dissolution inhibitors have been added to the photoresist polymers to form a two-component system. However, the increased amount of the dissolution inhibitor [about 30 %(w/w) of the resin) resulted in, among others, poor reappearance, high production cost, poor adhesiveness, and a severe top-loss of the resist in the etching process resulting in a poor pattern formation.
Despite these difficulties, a variety of photoresist polymers with improved etching resistance, adhesiveness and resolution have been developed. Unfortunately, however, most chemically-amplified photoresists currently available have a relatively short post exposure delay (PED) stability. In general, when there is delay between exposure of the photoresist to light and development of the exposed photoresist, acids that are generated on the exposed area are neutralized by amine compounds which may be present in the production atmosphere. Since the pattern formation depends on acids that are generated by the exposure, neutralization of acids by atmospheric amine compounds reduce, prevent or alter a pattern formation, e.g., a T-topping phenomenon may occur where the top portion of the pattern forms a T-shape.
Therefore, there is a need for a photoresist polymer having an excellent etching properties, heat resistance and enhanced PED stability.
An object of the present invention is to provide a novel PR polymer having an excellent etching and heat resistance, and an enhanced PED stability. The present inventors have found that a polymer derived from a monomer comprising a bicyclo compound has an excellent etching and heat resistance, and an enhanced PED stability.
Another object of the present invention is to provide PR polymers using the PR monomers described above and a process for preparing the same.
Another object of the present invention is to provide photoresist compositions using the PR polymers described above, and a process for preparing the same.
Still another object of the present invention is to provide a semiconductor device produced by using the PR composition.
The present invention provides a bicyclic PR monomers comprising an amine functional group and an acid labile protecting group. In particular, bicyclic PR monomers of the present invention are compounds of the formula: 
where B is selected from the group consisting of moieties of the formula: 
R is hydrogen, substituted or non-substituted (C1-C10) straight or branched chain alkyl, cycloalkyl, alkoxyalkyl, cycloalkoxyalkyl, xe2x80x94COORxe2x80x2, xe2x80x94(CH2)tOH, xe2x80x94COO(CH2)tOH or a moiety of the formula: 
each of V and W is independently substituted or non-substituted (C1-C10) straight or branched chain alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl;
Rxe2x80x2 is hydrogen, substituted or non-substituted (C1-C10) straight or branched chain alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; Rxe2x80x3 is an acid labile protecting group;
each of R1-R12 is independently hydrogen, substituted or non-substituted (C1-C10) straight or branched chain alkyl, cycloalkyl, alkoxyalkyl, cycloalkoxyalkyl, xe2x80x94CH2OH or xe2x80x94CH2CH2OH;
n is an integer from 1 to 3: and
each of d, m and t is independently an integer from 0 to 5.
The acid labile protecting group is preferably selected from the group consisting of tert-butyl, tetrahydropyran-2-yl, 2-methyl tetrahydropyran-2-yl, tetrahydrofuran-2-yl, 2-methyl tetrahydrofran-2-yl, 1-methoxypropyl, 1-methoxy-1-methylethyl, 1-ethoxypropyl, 1-ethoxy-1-methylethyl, 1-methoxyethyl, 1-ethoxyethyl, tert-butoxyethyl, 1-isobutoxyethyl and 2-acetylmenth-1-en-1-yl.
Particularly preferred bicyclo PR monomers of the present invention are: 2-(1-tert-butoxycarbonylpiperidin-2-yl)ethyl 5-norbornene-2-carboxylate: 
2-(1-tert-butoxycarbonylpiperidin-2-yl)ethyl 5-norbomnene-2,3-dicarboxylate: 
2-(1-tert-butoxycarbonylpiperidin-2-yl)ethyl, 3-tert-butyl 5-norbornene-2, 3-dicarboxylate: 
2,3-di[(1-tert-butoxycarbonylpiperidin-2-yl)ethyl]5-norbomene-2,3-dicarboxylate; 
The compound represented by Chemical Formula 1 can be prepared by a variety of methods. In one method of preparing compounds of formula 1, which is particularly useful for compounds 1 where R is hydrogen or substituted or non-substituted (C1-C10) straight or branched chain alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl, the method comprises:
(al) reacting a diene compound of the formula: 
with an acrylate of the formula:
to produce a bicyclic carboxylic acid of the formula: 
where R is hydrogen or substituted or non-substituted (C1-C10) straight or branched chain alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; and n is an integer from 1 to 3;
(b1) reacting the bicyclic carboxylic acid 8 with thionyl chloride (SOCl2), preferably in an equal molar amount; and
(c1) reacting the product of step (b 1) with a hydroxy compound of the formula: 
to produce the desired compound 1, where B, V and m are those defined above.
In particular, compound 6 is dissolved in an organic solvent and cooled to temperature in the range of from about xe2x88x9235xc2x0 C. to about xe2x88x9225xc2x0 C., and compound 7 is slowly added to the mixture. The resulting reaction mixture is stirred for about 8 to 12 hours at temperature in the range of from about xe2x88x9235xc2x0 C. to about xe2x88x9225xc2x0 C. After which the reaction temperature is allowed to reach room temperature. The resulting mixture is stirred for additional about 8 to 12 hours. Compound 8 can be recovered by a standard work-up followed by concentration of the resulting organic phase.
In the step (c1) above, triethylamine, preferably in an equal molar amount, is added to the reaction mixture to neutralize any acids that is formed in the reaction mixture. An aqueous work-up followed by drying the organic phase, filtering, and removing the organic solvent, e.g., by vacuum distillation, provides the desired compound.
In another method of preparing compounds of formula 1, which is particularly useful for compounds 1 where R is COORxe2x80x2 or a moiety of the formula 
the method comprises:
(a2) reacting a diene compound of formula 6 with maleic anhydride to produce 5-norbornene-2,3-dicarboxylic anhydride;
(b2) (i) when R is COORxe2x80x2, contacting said 5-norbornene-2, 3-dicarboxylic anhydride with ROH in the presence of an acid catalyst to produce a 5-norbornene-2,3-dicarboxylate compound; or (ii) when R is 
xe2x80x83hydrating said 5-norbomene-2,3-dicarboxylic anhydride to produce a 5-norbomene-2, 3-dicarboxylic acid; and
(c2) reacting the 5-norbornene-2,3-dicarboxylate compound or 5-norbomene-2,3-dicarboxylic acid with a hydroxy compound of formula 9 to produce the desired compound 1, where B, W, Rxe2x80x2 and d are those defined above.
More specifically, in the step (a2) above, compound 6 is dissolved in an organic solvent and cooled at temperature in the range of from about xe2x88x9235xc2x0 C. to about xe2x88x9225xc2x0 C. Maleic anhydride, preferably in a solution and in an equal amount, is slowly added to the resulting solution. The reaction mixture is then stirred for about 8 to 12 hours at temperature in the range of from about xe2x88x9235xc2x0 C. to about xe2x88x9225xc2x0 C. After which the reaction temperature is allowed to reach room temperature. The reaction mixture is stirred for additional about 8 to 12 hours, and the 5-norbornene-2,3-dicarboxylic anhydride is obtained after removing the organic solvent. And, when the R is 
the step of (c2) comprises reacting the hydroxy compound 9, preferably in an amount which is double the theoretical amount (in moles) of the 5-norbomene-2,3-dicarboxylate compound, in the presence of triethylamine, preferably in the amount equal to the amount of the hydroxy compound 9. Aqueous work-up followed by drying the organic phase, filtering and concentrating, e.g., by vacuum distillation, then provides the desired compound of formula 1. While any non-protic organic solvent can be used in the steps (a1) or (a2) above, preferred organic solvents include tetrahydrofuran (THF), dimethylformamide, dimethylsulfoxide, dioxane, benzene, toluene and xylene.
The present invention also provides a PR copolymers which is derived from a monomer comprising a compound of formula 1. The PR copolymer according to the present invention can further comprise a second monomer selected from compounds of the formulas: 
and mixtures thereof;
where R13 is substituted or non-substituted (C1-C10) straight or branched chain alcohol; R4 is an acid labile protecting group; R15 is hydrogen or xe2x80x94COOH; and a, b, and c are independently an integer from 1 to 3. The copolymer of the present invention can further comprise maleic anhydride as a third monomer.
Preferably, the PR copolymer of the present invention has a molecular weight in the range of from about 3000 to about 100,000. Moreover, the PR copolymer of the present invention comprises the following copolymer:
poly(tert-butyl 5-norbomene-2-carboxylate/2-hydroxyethyl 5-norbornene-2-carboxylate/5-norbomene-2-carboxylic acid/2-(1-tert-butoxycarbonylpiperidin-2-yl)ethyl 5-norbornene-2-carboxylate/maleic anhydride): 
Poly(tert-butyl 5-norbornene-2-carboxylate/2-hydroxyethyl 5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/2-(1-tert-butoxycarbonylpiperidin-2-yl)ethyl 5-norbornene-2,3-dicarboxylate/maleic anhydride): 
Poly(tert-butyl 5-norbomene-2-carboxylate/2-hydroxyethyl 5-norborene-2-carboxylate/5-norbornene-2-carboxylic acid/2-(1-tert-butoxycarbonylpiperidin-2-yl)ethyl, 3-tert-butyl5-norbornene -2,3-dicarboxylate/maleic anhydride): 
Poly(tert-butyl 5-norbomene-2-carboxylate/2-hydroxyethyl 5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/2,3-di[(1-tert-butoxycarbonylpiperidin-2-yl)ethyl]5-norbomene-2,3-dicarboxylate/maleic anhydride): 
Poly(tert-butyl 5-norbornene-2-carboxylate/2-hydroxyethyl 5-norbomene-2-carboxylate/5-norbornene-2,3-dicarboxylic acid/2,3-di[(1-tert-butoxycarbonylpiperidin-2-yl)ethyl]5-norbornene-2,3-dicarboxylate/maleic anhydride): 
In the above Chemical Formulas 13 to 17, the ratio of v:w:x:y:z is preferably 0.01 to 99 mol %:0.01 to 99 mol %:0.01 to 35mol %:0.01 to 35mol %:0.01 to 99 mol %.
The copolymer of the present invention can be prepared by radical polymerization of monomers with a conventional radical polymerization initiator. An exemplary procedure for preparing copolymers of the present invention includes the steps of:
(a) admixing
(i) a compound of formula 1,
(ii) a second monomer selected from the group consisting of compounds of formulas 10, 11, 12, and mixtures thereof,
optionally (iii) maleic anhydride,
(iv) a polymerization initiator; in an organic solvent; and
(b) polymerizing the admixture under an inert atmosphere, preferably under nitrogen or argon atmosphere.
The polymerization can be carried out by either a bulk polymerization or a solution polymerization. Exemplary solvents suitable for polymerization include cyclohexanone, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, dioxane, methyl ethyl ketone, benzene, toluene and xylene.
Exemplary polymerization initiators include any conventional radical polymerization initiators such as benzoylperoxide, 2,2xe2x80x2-azobisisobutyronitile (AIBN), acetylperoxide, laurylperoxide, tert-butylperacetate, tert-butylhydroperoxide and di-tert-butylperoxide. Preferred polymerization temperature is in the range of from about 40xc2x0 C. to about 90xc2x0 C., and a preferred polymerization reaction time is in the range of from about 4 hours to about 20 hours.
The present invention also provides a PR composition comprising the PR copolymer of the present invention, an organic solvent, and a photoacid generator.
Preferred photoacid generators include sulfides and onium type compounds. In one particular embodiment of the present invention, the photoacid generator is selected from the group consisting of diphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate, diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate, diphenyl p-tert-butylphenyl triflate, triphenylsulfonium hexafluororphosphate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate and dibutylnaphthylsulfonium triflate. Typically, the amount of photoacid generator used is from about 0.05% by weight to about 10% by weight of the photoresist resin employed. It has been found that when the photoacid generator is used in the amount less than about 0.05%, it lowers photosensitivity of the PR composition, and when the photoacid generator is used in the amount greater than about 10%, it results in poor patterning due to its large absorption of DUV (Deep Ultra Violet).
Exemplary organic solvents suitable in PR compositions of the present invention include methyl 3-methoxypropionate, ethyl 3-ethoxypriopionate, propylene glycol methyl ether acetate, cyclohexanone, 2-heptanone and (2-methoxy)ethyl acetate.
The amount of solvent used is preferably in the range of from about 200% to about 1000% by weight of the PR resin (i.e., copolymer). This ratio has been found to be particularly used in obtaining a photoresist layer of desirable thickness when coated on to a suitable substrate such as a silicon wafer in production of a semiconductor element. In particular, it has been found by the present inventors that when the amount of organic solvent is about 600% by weight of the PR copolymer, a PR layer having 0.5 xcexcm of thickness may be obtained.
The PR composition is prepared by dissolving the copolymer of the present invention in an organic solvent to the amount of about 10% to about 30% by weight of the solvent, adding the photoacid generator in the amount of from about 0.05% to about 10% by weight of the copolymer, and filtering the resulting composition through a hyperfine filter. The PR composition prepared by the present invention has an excellent etching resistance, adhesiveness and heat resistance. Also, its remarkably enhanced PED stability makes it very useful as ArF photosensitive film.
The present invention provides the method for forming the PR pattern as follows: (a) coating the above described photoresist composition on a substrate of semiconductor element to form a photoresist film; (b) exposing the photoresist film to light using a light source; and (c) developing the photoresist film, for example, using an alkaline solution such as 2.38 wt % TMAH solution. Optionally, the photoresist film can be heated (i.e., baked), preferably to temperature in the range of from about 70xc2x0 C. to about 200xc2x0 C., before and/or after the step (b).
Exemplary light sources which are useful for forming the PR pattern include ArF (193 nm), KrF (248 nm), VUV (157 nm), EUV, E-beam, X-ray and ion beam. Preferably, the irradiation energy is in the range of from about 1 mJ/cm2 to about 100 mJ/cm2.
The present invention also provides a semiconductor device, which is manufactured using the photoresist composition described above.